Source -Another month, another set of data that shows the main browser usage trend is unchanged: though its lead remains large, Internet Explorer is still losing ground to all other browsers. Firefox is steadily gaining, Safari remains in a nonthreatening third place, Chrome is happily carving out a small niche for itself, and poor Opera can't seem to budge from fifth place. In September, all browsers except for IE showed positive growth. In fact, IE experienced the biggest drop in recent memory.
September 2009 browser stats: IE sees biggest drop yet - Ars Technica